Prior to writing this article we had no idea that the quality of our indoor air was so polluted by things we normally have in our houses. Common sense tells us that, ideally, by cleaning, source control, and cross ventilation (with clean air, ha!) we can improve the quality of the air in our homes.

According to the EPA, if the measures you’ve been taking to clean your indoor air have just not cut it, then air purifiers may be useful. They come in handy because they are designed to remove particulate matter (PM) or gases. Some purifiers even destroy, degrade, or transform the pollutants that pass through the filter.

We interviewed Dr. Petros Koutrakis from the Harvard T.H. Chan School of Public Health, who had some noteworthy insight. Dr. Koutrakis’s career has focused on researching the development of human exposure measurement techniques on air pollutants. He is also the Head of the Exposure, Epidemiology and Risk Program, and the Director of the EPA/Harvard University Center for Ambient Particle Health Effects.

Asked to comment about the effects of air pollution in the US, Dr. Koutrakis stated: “We have found that it can contribute to mortality, cause inflammation, and cause changes in heart, lung, and cognitive function, and other adverse health outcomes. So there are many studies that show the effects of pollution, specifically particles, even in low concentrations. We used to think that although high pollution was bad for you, low pollution was ok. But now, we find that even at levels near the National Air Quality Standards, people may not be sufficiently protected.”

The two main factors that affect the quality of our indoor air are particulate matter (PM) and gases. The US Environmental Protection Agency classifies PM as particles suspended in the air ranging from ultrafine, fine, and coarse. The types of PM alive and well in our household air include human skin flakes, dust, smoke, fumes, outdoor contaminants, viruses, bacteria, pollen, spores, dust mites, cockroach body parts and droppings, and animal dander.

Inhaled over a significant period of time, fine particles, emitted through tobacco smoke, chimneys, unvented appliances, fireplaces, printers, incense, candles, and even traffic emissions, can pose a threat to respiratory health by causing acute or chronic health conditions. As for gaseous pollutants, they are not attached to any particles per se. They include carbon monoxide and nitrogen dioxide.

Suggestions For Improving Your Indoor Air

As we mentioned previously, air cleaning, source control, and cross ventilation are supposed to help in keeping the air fresh. Here are measures you can take to make your indoor air cleaner:

  • Air cleaning with an air purifier used in tandem with source control and ventilation has proven to be effective. That is, as long as other factors such as the cleaning and proper ventilation are being kept up as well.
  • Source control by removing the pollutants individually using methods such as having smokers only smoke outside and making sure your humid bathroom is being properly cleaned and ventilated.
  • Cross ventilation with outdoor air is a great way to dilute permeating residential air pollutants. Given that the outside air coming in is relatively clean, this can be complemented with the air purifier. Also, don’t keep your windows open on high pollution days. You can keep track of the air quality in your state at the American Lung Association’s State Of The Air report, available here.
  • Avoiding scents and mothballs made with paraffin wax, such as air fresheners and scented candles, which release toxic compounds. Plus, according to UC Berkeley’s School of Public Health, green air fresheners are not any safer than regular ones.
  • When using nail polish, acetone, perfumes, and hair spray, make sure you’re in a ventilated area with fresh air coming in.
  • For fabrics, make sure you always wash any new garments, linens, and towels before using them. This will remove unwanted chemicals. For dry-cleaned clothes, make sure to air them out outside, as these can raise the air pollution levels in the home.
  • Clean often. Wipe down surfaces where dust settles, vacuum the carpets, sweep and mop, keep your air filters up to date and remember to clean the furnace and the chimney (if you have one it must be cleaned annually.)

The Science Behind Air Purifiers

Portable air purifiers are built to clean single rooms or large spaces, but not entire houses with extensive square footage. For instance, if you live in a studio apartment that is within the parameters of what they air purifier cleans, then wonderful: you got yourself a purifier to clean your entire place of pollutants.

The companies we’ve reviewed manufacture portable purifiers that can be conveniently moved wherever you need them to clean. And for it to give you the best bang for your buck, you must place it in the right location.

You’d think that placing the purifier in the middle of your room would be your best bet. But according to our research, the principle of diffusion says that moving particles will move through your room while keeping an equal distance from each other. The air purifiers we’ve reviewed here have both a filter and a fan that creates a vacuum to pull the particles from the air. Therefore, placing the purifier at the end of one room in an unobstructed position is ideal. See below:

To find out more about the science and testing standards of air purifiers, we reached out to Jill Notini, VP of Communications and Marketing at the Association of Home Appliance Manufacturers, or AHAM.

For context, AHAM is a trade association that represents the manufacturers of home appliances, including the manufacturers of air cleaners sold in the United States. Through them, a program called AHAM Verifide was developed to certify appliances that have passed set standards of operation. That’s why you will see, when shopping around for a purifier, that some—like the GermGuardian AC4825W pictured below—have the AHAM Verifide seal of approval.

Screenshot from, November 2019

According to Mrs. Notini: “The AHAM Verifide program is a certification and verification program for portable room air cleaners. What we do through that program is to provide initial and follow up verification testing in the performance of portable room air cleaners. So we measure the reduction rates of tobacco smoke, dust, and pollen for each air cleaner that is tested. Tobacco smoke, dust, and pollen are representative of different sized particles that may be in your room. Tobacco smoke is a very small particle so we use that to represent the very low end of particle size, so it could also represent smoke from fires. For instance, what’s happening in California with wildfires. And then it goes all the way up to the largest particle size which is pollen, a particle you can actually see in the air.”

For each air cleaner that AHAM tests, they provide the manufacturers with the data that they’re required to put on the label on the product packaging. The manufacturers have to declare a room size that the unit would best work in and declare the CDR (Cleaner Delivery Rate) for tobacco smoke, dust, and pollen. Then, as a consumer, you can compare side by side the cleaning ability of each model.

Air cleaner manufacturers use a variety of technologies. Some will use a HEPA filter, while others will use electrostatic filters which charge the particles, or even a combination of technologies in order to effectively reduce airborne particulates. What’s more, air purifiers also vary in price, design, and size. For this reason, it can get confusing for consumers to look at different air cleaner options.

Regarding this potential confusion, Mrs. Notini explained that: “What we’re trying to do is to level the playing field by saying ‘ok we’re gonna run this test so that all air cleaners are evaluated in the same way and that we can help consumers from one air cleaner to the next know how to look for the right cleaner for their room.’ ”

Can Indoor Plants Actually Purify Your Air?

The 1989 NASA indoor pollution study by researcher Bill Wolverton put plants on the map as an alternative for air purification.

In the study, Wolverton discovered that houseplants that require low light demonstrated the potential to improve air quality by removing benzene, trichloroethylene, and formaldehyde from the air in trace amounts. Turns out the best plants for air purification are bigger in size and leaf surface area.  Because of this, some scientists agree that plants have the potential for improving air quality by removing volatile organic compounds from the air.

We asked Dr. José Fumero, plant ecologist and professor at the Ana G. Méndez University in Puerto Rico, what his take was on the plant purification debate. He commented that: “The NASA study was conducted in a closed chamber, and under these conditions, they observed that, yes, plants remove certain contaminants, one of them being benzene. Some of those contaminants can be generated within the home through electro-domestic appliances and also by the use of chemical substances inside the home. But the study does have a flaw and it’s that it was done in a closed chamber. If you’re gonna have just one plant in your home that’s not gonna help in anything. It’s true that you need many plants [to feel the purification effects.]”

So far, no study has been done in a setting that mimics an actual household with open windows. Therefore, we can’t accurately say how many plants per square feet you’d need to purify any given room. That is, without taking into account open doors and windows.

For his part, Wolverton recommends the golden pothos (also known as Devil’s Ivy because it refuses to die) as a starter plant.

In conclusion, plants have proven to purify the air in closed testing but not in open spaces. There are many benefits to owning plants, as they can help in reducing stress and improving your mood. Dr. Fumero goes on to say: “In my understanding, it is positive because they absorb something. The problem is obviously they don’t work as a filter. Although they can assimilate, they don’t create an air draft. But I do think it’s beneficial to have indoor plants.”